Which of these best describes genetic drift?
a. decrease in mutation rate
b. selection of favorable genes
c. increase in species adaptation
d. random change in gene frequency

Genetic drift is a change in the frequency of alleles in a population as a result of random sampling of organisms. For example, imagine you have two different alleles in the population responsible for white and purple color of a flower. Their allele frequencies are 0.6 for white flowers and 0.4 for purple flowers. After some change in the environment, only purple flowers survive. They will reproduce, and in the population there will be only purple flowers. The population for these flowers will increase from 0.4 to 1.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.